How to find the source of wi-fi interference?

Question

WiFi

There is one office - an average room (open space) with about 70 employees. 2 access points cisco WAP4410N.
So everyone is connected to the network via a wire, but many have mobile devices, and at meetings, management works with laptops via wi-fi.
For the second day in a row, there is a problem with WI-FI: very poor connection, very often interrupted, pings to access points jump up to 4000ms, when connecting to a point on Windows, network identification takes a very long time. Access points are powered by POE. after rebooting the points, the connection is established but not for a long time, then the pings start growing again until they completely disappear. It happens in 10 minutes.
It all happens at about the same time: from morning until 5-6 pm somewhere.
The only guess what the problem is - external interference from some equipment nearby.
Hence the questions: if my assumption is correct, then how can this source of interference be calculated? Is it possible to do this with the resources (and finances) of the IT department of a small company? Or maybe there are some commercial offices that do this?
Or maybe I'm digging in the wrong direction at all, and the problem has a completely different reason?
UPD:
In general, thanks to everyone for the answers, the problem disappeared by itself (for a long time), which confirms my version of external interference.

Answer 1

It all happens at about the same time: from morning until 5-6 pm somewhere.

That's your reason - people. See your broadcast, how crowded it is, how close the points are from each other, on which channels your points intersect (you didn’t make both points on channel 6?) and see the load on the channel / vlan wi-fi network
in the office:
1. if possible, scattered it on channels 1 and 11
2. reduced the power of the point, since the office building and everyone clog the air. at reduced power, there is less interference from neighboring access points
3. assigned big bosses binding by MAC and anlim in speed, and for everyone else - for example 512kbps
4. roughly estimate the Fresnel zones (roughly speaking, the number and range of interference from the signal source)
5. Vuyalya) works fine)) (wifi - Ubiquity, controller - their own, soft, on JVM on a Linux machine)
Utility: Look towards wavemon - Linux's little utility, but very useful in diagnosing problems

Answer 2

Roskomnadzor has the necessary equipment. But this is not a cheap pleasure.